This application claims the priority of Korean Patent Application No. 2003-23726, filed on Apr. 15, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a projection display that projects an enlarged image onto a screen.
2. Description of the Related Art
In recent years, projection displays that project an enlarged image, which has been modulated by an optical modulator such as a liquid crystal panel, onto a screen have become popular.
FIG. 1 is a schematic diagram illustrating the configuration of a conventional projection display.
Referring to FIG. 1, a conventional projection display comprises a liquid crystal panel 20 which is an optical modulator, an illumination module 10 for emitting light to the liquid crystal panel 20, and a projection lens 40 for projecting a modulated image on an enlarged scale.
The projection display includes three liquid crystal panels 20R, 20G and 20B corresponding to colored images, namely, red (R) image, green (G) image and blue (B) image, respectively. Reference numeral 30 represents a synthesis prism which synthesizes light which has been modulated by the liquid crystal panels 20R, 20G and 20B to respectively correspond to colored images, and radiates the light to the projection lens 40.
The illumination module 10 includes a light source 1, an integrator 3, a condenser lens 4, a plurality of mirrors 5R, 5G, 5B, and 6, and a plurality of relay lenses 7 and 8.
A metal halide lamp, a high pressure mercury lamp, or the like, is used as the light source 1. The light source 1 is positioned at a focal point of a reflecting mirror 2 having a paraboloidal surface to obtain parallel light. The integrator 3 is used to uniformly illuminate the liquid crystal panels 20R, 20G and 20B. In general, a couple of fly-eye lenses which are formed in a two-dimensional micro lens are used as the integrator 3. Light which has been passed through the integrator 3 is focused by the condenser lens 4. The mirrors 5R, 5G and 5B are selective reflecting mirrors which reflect red light, green light and blue light, respectively, and transmit other colors of light. Light is divided into red light, green light and blue light while passing through the mirrors 5R, 5G, and 5B. Three lights are passed through the relay lenses 7 and 8, and are incident on the liquid crystal panels 20R, 20G and 20B, respectively. The liquid crystal panels 20R, 20G and 20B modulate the incident light and output R, G and B images. Light respectively emitted from the liquid crystal panels 20R, 20G and 20B is synthesized by the synthesis prism 30 and projected, on an enlarged scale, by the projection lens 40.
The life span of a lamp which is used as the light source of the conventional projection display is several thousands of hours at the longest. Therefore, when the conventional projection display is used a lot, it has a drawback in that the lamp should be replaced often. The conventional projection display has another drawback in that a plurality of mirrors and lenses are used and accordingly an illumination module is quite large.
Japanese Patent Laid-open Publication No. 2001-42431 discloses an illumination module using a light emitting diode (LED), which also requires lots of lenses and mirrors. Thus, there is a limit to downsizing the illumination module.